SiC being silicon carbide has all of a band gap, dielectric breakdown electric field strength, a saturated drift velocity, and heat conductivity relatively greater than those of silicon (Si). Thus, SiC power devices allow for significant reduction in a loss of power and for size reduction, and the SiC power devices can achieve energy conservation upon conversion of power supply and electric power, thereby attracting attention for enhanced performance of electric vehicles, enhanced functionality of solar cell systems, or the like to achieve a low-carbon society.
To manufacture the SiC power device, a SiC epitaxial layer being an active region of the device needs to be epitaxially grown on a SiC bulk substrate by a thermal chemical vapor deposition (CVD) or the like in advance. The active region herein is a cross-sectional region including a growth direction axis in which a doping density in crystals and a film thickness are precisely controlled according to desired device specifications. The SiC bulk substrate including the SiC epitaxial layer formed thereon is referred to as a silicon carbide (SiC) epitaxial wafer. The SiC power device is required to have high voltage specifications of, for example, several hundreds of V to several tens of kV, so that a film thickness of the SiC epitaxial layer needs to be thickly formed to be several μm to several hundreds of μm. Defects occurring on a surface of the SiC epitaxial layer being the active region degrade characteristics of the device, so that it is desired to reduce a defect density of the SiC epitaxial layer more than that of the SiC bulk substrate.
For the epitaxial growth of the SiC, a step-flow epitaxy in which the SiC bulk substrate having an off-angle of more than 0° is grown by the thermal CVD is typically performed. Surface defects, such as an abrasive scratch and fine irregularities, on the surface of the SiC bulk substrate are easily transferred to the SiC epitaxial layer. To suppress the transfer of the surface defects on the SiC bulk substrate, lowering a growth temperature in an early stage of the SiC epitaxial growth to slow down a growth speed is effective. However, the SiC epitaxial layer needed to have the thick film is preferably grown at a high temperature to speed up the growth speed for improving throughput in manufacturing the SiC epitaxial wafer.
Thus, a method for manufacturing a SiC epitaxial wafer by performing a first epitaxial growth at a temperature of lower than 1500° C. and then performing a second epitaxial growth at a temperature of 1500° C. or higher has been developed (for example, see Patent Document 1). The conventional method lowers the growth temperature for the purpose of suppressing a transfer of surface defects from a SiC bulk substrate in the first epitaxial growth, and increases the growth temperature for the purpose of performing the second epitaxial growth at high speed on the SiC epitaxial layer formed by the first epitaxial growth.